The field of the invention relates to methods and apparatus for assembling syringes and other such medical devices which include a stopper and plunger assembly for drawing or ejecting fluids.
Syringes are generally comprised of a cylindrical barrel, a cannula secured to one end of the barrel, a stopper within the barrel, and a plunger secured to the stopper for moving it within the barrel. The barrel, plunger and stopper are often molded from various thermoplastic materials. The cannula is usually made from metal such as stainless steel.
The manufacture of syringes typically involves the use of a machine for assembling the barrel/cannula assembly with the other molded components. Barrel/cannula assemblies, complete with shields for protecting the cannulas, are loaded into the machine while plungers and stoppers are loaded into separate machine feed hoppers. The stoppers flow to a feed bowl or the like from where they are fed to a track and then to a dial. A dial is a disk shaped metal (or non-metal) article having slots for retaining selected items. In the meantime, the plungers move along a track to another dial adjacent to the stopper dial but at a different height within the machine. The plungers and stopper held by the respective dials are moved into engagement with each other and joined. This subassembly is then transferred to another dial from where it is inserted within the syringe barrel.
It is important to provide lubrication between the stopper and the inner wall of the syringe barrel so that the syringe can be operated smoothly. A medical grade of silicone oil or lubricant has typically been applied directly to the inner walls of the syringe barrel prior to insertion of the plunger/stopper subsassembly. This technique has several drawbacks, however. One is the risk of placing more silicone oil into the barrel than is necessary for the proper functioning of the syringe assembly. This may alter test results on fluids, such as blood, collected within the syringe or possibly compromise drug therapy. In addition to slowing down the assembly process, there is also the risk of excess oil falling on parts of the assembly machine, thereby necessitating more frequent cleaning.